In light of the recent social demand for saving energy and resources, tires are now required to have high durability. To respond to this demand, rubber materials with high breaking resistance and abrasion resistance are also desired commonly. Further, a surge in natural rubber prices has created a need for developing synthetic rubber that exhibits durability equal to that of natural rubber.
To enhance durability of the synthetic rubber, the cis content of synthetic polyisoprene is conventionally increased to improve strain-induced crystallinity. Refer, for example, to JP 2006-503935 A (PTL 1) and JP S53-090391 A (PTL2).
However, the durability of the crosslinked rubber composition obtained with use of the conventional synthesized polyisoprene is not sufficient.